I use a MS trackball. When cursor is over any image, the scroll wheel reduces or enlarges it.
I believe what Andy and James says is true, it is NOW an IE plugin. Anyone who has taken 'windows updates' in the past 6 months will have the latest version of IE with the function. However, OEM disks with machines being currently sold dont have the latest version. Could be Greg's new machine actually has an older version than his older machine.